What does it mean when the heater is turned on with A/C?
2 Answers
Turning on the heater with A/C means the car's compressor is running, which will additionally increase the vehicle's fuel consumption. Reasons why turning on the heater with A/C increases fuel consumption: In A/C mode, since the car's air conditioning compressor is always in operation, it will inevitably lead to increased fuel consumption and additional engine load. When using the heater, the A/C switch should be turned off to prevent the compressor from running and causing extra fuel consumption during heating. Function of A/C: A/C is the abbreviation for air conditioning, with its full name being air condition, which can be understood as air control or air adjustment. It achieves the purpose of cooling or heating through different operation modes of the air conditioning compressor, hence it has dual meanings of cooling and heating. However, in cars, since the heating function of the vehicle's air conditioning is accomplished through the heat from the engine's cooling water and the heating wires on the glass, A/C only has the single meaning of cooling in this context.
Turning on the A/C button while using the heater means activating the air conditioning compressor during heating mode. Having driven several car models, I find this trick particularly useful. The primary purpose is dehumidification and defogging—for instance, when driving in winter or rainy conditions, if the windshield fogs up, relying solely on the heater takes a long time to clear. But with the A/C button engaged, the compressor and blower dry the air rapidly, clearing fog almost instantly while improving cabin comfort. Of course, running the compressor slightly increases fuel consumption, so it’s unnecessary to keep it on continuously. You can manually control it or let an automatic climate system adjust temperatures for switching. My tip: turn it on for a few minutes during heavy fogging, then deactivate A/C once cleared—this saves fuel and enhances safety. Experiment with your car’s system, as brands differ (e.g., Japanese cars defog faster).
